A Ledger is derived from a Journal by applying a filter specification
to select Transactions and Postings of interest. It contains the
filtered journal and knows the resulting chart of accounts, account
balances, and postings in each account.

Filter a journal's transactions as specified, and then process them
to derive a ledger containing all balances, the chart of accounts,
canonicalised commodities etc.
Like journalToLedger but uses the new matchers.